I was then posting such a thing 😄
Your most likely suspect for the poor fuel economy will be the near constant DPF regenerations, when you first got the car and done the 200 mile trip, it should have in theory been able to passively clear the soot, or put itself into an active regen mode to inject more fuel to burn off the accumulation of soot particles. After an hour of trying to clear the DPF, or if the soot will not clear in that time while driving at motorway speeds, then it will put on the exhaust light, the next stage is exhaust light with limp mode.
Now in Km, you usually check oil ash at 230k Km, then every 30k thereafter as a rule of thumb. This is not a measured value, but one that the ECU calculates, however if a car is burning more oil than average, then the 'real' value will be beyond what is claimed (by how much, you can only guess) as this value increases, the efficiency of the DPF goes out of the window, as it clogs the exhaust. This creates more back pressure, making the car work harder = more fuel.
The next thing that occurs is the soot from unburnt fuel, this is what the DPF can actually burn off, but only if it is working correctly.
I would recommend you try to locate someone in your area that you can plug in your car and read out the following value in the engine ECU
Oil Ash
Soot measured
Soot calculated
You could in theory, if the person is happy to help, do what's called a 'static regeneration' on the DPF
Kinda noisy, so would recommend that you drive to a car park for example or layby where you can perform this process, make sure you have plenty of fuel in the car
While you have VCDS, you can check in the gateway of the car, and make sure the battery is adapted.
Most important are battery type: AGM / EFB / Wet *names in coding vary from the values
And the Ah rating of the new fitted battery, then last is to increase the serial number by 1 to make the car know it's a fresh battery.